1. Field of the Invention
This invention relates generally to oilfield downhole tools and more particularly to drilling assemblies utilized for drilling wellbores in which electrical power and data are transferred between rotating and a non-rotating sections of the drilling assembly.
2. Description of the Related Art
To obtain hydrocarbons such as oil and gas, boreholes or wellbores are drilled by rotating a drill bit attached to the bottom of a drilling assembly (also referred to herein as a xe2x80x9cBottom Hole Assemblyxe2x80x9d or xe2x80x9cBHAxe2x80x9d). The drilling assembly is attached to the bottom of a tubing, which is usually either a jointed rigid pipe or a relatively flexible spoolable tubing commonly referred to in the art as the xe2x80x9ccoiled tubing.xe2x80x9d The string comprising the tubing and the drilling assembly is usually referred to as the xe2x80x9cdrill string.xe2x80x9d When jointed pipe is utilized as the tubing, the drill bit is rotated by rotating the jointed pipe from the surface and/or by a mud motor contained in the drilling assembly. In the case of a coiled tubing, the drill bit is rotated by the mud motor. During drilling, a drilling fluid (also referred to as the xe2x80x9cmudxe2x80x9d) is supplied under pressure into the tubing. The drilling fluid passes through the drilling assembly and then discharges at the drill bit bottom. The drilling fluid provides lubrication to the drill bit and carries to the surface rock pieces disintegrated by the drill bit in drilling the wellbore. The mud motor is rotated by the drilling fluid passing through the drilling assembly. A drive shaft connected to the motor and the drill bit rotates the drill bit.
A substantial proportion of the current drilling activity involves drilling of deviated and horizontal wellbores to more fully exploit the hydrocarbon reservoirs. Such boreholes can have relatively complex well profiles. To drill such complex boreholes, drilling assemblies are utilized which include a plurality of independently operable force application members to apply force on the wellbore wall during drilling of the wellbore to maintain the drill bit along a prescribed path and to alter the drilling direction. Such force application members may be disposed on the outer periphery of the drilling assembly body or on a non-rotating sleeve disposed around the rotating drive shaft. These force application members are moved radially to apply force on the wellbore in order to guide the drill bit and/or to change the drilling direction outward by electrical devices or electro-hydraulic devices. In such drilling assemblies, there exists a gap between the rotating and the non-rotating sections. To reduce the overall size of the drilling assembly and to provide more power to the ribs, it is desirable to locate the devices (such as motor and pump) required to operate the force application members in the non-rotating section. It is also desirable to locate electronic circuits and certain sensors in the non-rotating section. Thus, power must be transferred between the rotating section and the non-rotating section to operate electrically-operated devices and the sensors in the non-rotating section. Data also must be transferred between the rotating and the non-rotating sections of such a drilling assembly. Sealed slip rings are often utilized for transferring power and data. The seals often break causing tool failures downhole.
In drilling assemblies which do not include a non-rotating sleeve as described above, it is desirable to transfer power and data between the rotating drill shaft of a drilling motor and the stationary housing surrounding the drill shaft. The power transferred to the rotating shaft may be utilized to operate sensors in the rotating shaft and/or drill bit. Power and data transfer between rotating and non-rotating section having a gap therebetween can also be useful in other downhole tool configurations.
The present invention provides contactless inductive coupling to transfer power and data between rotating and non-rotating sections of downhole oilfield tools, including the drilling assemblies containing rotating and non-rotating members.
In general, the present invention provides apparatus and method for power and data transfer over a gap between rotating and non-rotating members of downhole oilfield tools. The gap may contain a non-conductive fluid, such as drilling fluid or oil for operating hydraulic devices in the downhole tool. The downhole tool, in one embodiment, is a drilling assembly wherein a drive shaft is rotated by a downhole motor to rotate the drill bit attached to the bottom end of the drive shaft. A substantially non-rotating sleeve around the drive shaft includes a plurality of independently-operated force application members, wherein each such member is adapted to be moved radially between a retracted position and an extended position. The force application members are operated to exert the force required to maintain and/or alter the drilling direction. In a preferred system, a common or separate electrically-operated hydraulic units provide energy (power) to the force application members. An inductive coupling transfers device transfers electrical power and data between the rotating and non-rotating members. An electronic control circuit or unit associated with the rotating member controls the transfer of power and data between the rotating member and the non-rotating member. An electrical control circuit or unit carried by the non-rotating member controls power to the devices in the non-rotating member and also controls the transfer of data from sensors and devices carried by the non-rotating member to the rotating member.
In an alternative embodiment of the invention, an inductive coupling device transfers power from the substantially non-rotating housing of a drilling motor to the rotating drill shaft. The electrical power transferred to the rotating drill shaft is utilized to operate one or more sensors in the drill bit and/or the bearing assembly. A control circuit near the drill bit controls transfer of data from the sensors in the rotating member to the non-rotating housing.
The inductive coupling may also be provided in a separate module above the mud motor to transfer power from a non-rotating section to the rotating member of the mud motor and the drill bit. The power transferred may be utilized to operate devices and sensors in the rotating sections of the drilling assembly, such as the drill shaft and the drill bit. Data is transferred from devices and sensors in the rotating section to the non-rotating section via the same or a separate inductive coupling. Data in the various embodiments is transferred by frequency modulation, amplitude modulation or by discrete signals.
Examples of the more important features of the invention thus have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto.